[rub] salt (in|into) the wound

to make a difficult or painful situation even worse for someone

The idiom "rub salt in the wound" originated from the literal act of adding salt to a wound, which is known to cause intense pain and discomfort. Figuratively, the idiom is used to describe a situation where someone does something that worsens another person's suffering, distress, or disappointment by highlighting or emphasizing their misfortune or failure.

I can't believe you would ask me to pay you back on the day that I got laid off.Thanks for rubbing salt in my wounds.
The fact that the Champions League is increasingly dominated by English clubs just rubs salt into his wounds.
The separation from Julie was already difficult for Alex.Mentioning her new boyfriend just rubbed salt into the wound.
To hold them to a standard that discriminatory marriage bans made impossible to meet rubs salt in the wound of their loss.